The Civil War was the central event of American history, and religion was central to the American Civil War experience. Religion did not cause the war, but it did magnify and intensify social, cultural, and political differences that contributed to sectional distrust and eventually disunion. Before the war, religious ideas informed the debates on slavery and the character and destiny of the Union; and, indeed, the divisions within religious bodies over the slavery issue both foretold secession and defined political loyalties during and after the war. When war came, religion gave Americans a rationale for fighting and dying, a means for understanding life and death, a moral compass, and institutional resources for providing relief to soldiers in the field and people suffering on the home front. Then, too, the civil religion of America as a chosen people gained greater force, if also one with regional permutations. The war also made possible African American aspirations for freedom and autonomy, which they expressed most powerfully in their own churches. Religion later helped rebuild the defeated South and explain defeat to white southerners, as it also spurred northern interest in Reconstruction, however imperfect and impermanent such interest proved to be.

From the antebellum period through the Civil War era, the United States was an overwhelmingly Protestant country, notwithstanding a growing Catholic presence almost everywhere and strong, if also numerically small, Jewish congregations in eastern seaboard cities. Protestantism largely defined the dominant American culture.